1. Field of the Invention
The present invention relates to a liquid container which can contain various liquids and an apparatus in which the liquid container is mountable. In particular, the present invention relates to a liquid container which is preferably used as an ink tank containing pigment ink, and an apparatus in which the liquid container is mountable and which is preferably used as a printing apparatus printing images using the pigment ink fed from the ink tank.
2. Description of the Related Art
An exemplary supply system for a print head of an ink jet printing apparatus is configured such that an ink tank which accommodates ink is removably connected to a terminal of the supply system. Known removable ink tanks include those which hold ink using a capillary force generating member such as a sponge provided inside the tank and those which hold ink directly inside a flexible bag or a rigid housing. In particular, printers for graphic art such as posters involve a large amount of ink supplied per sheet and thus require a large ink capacity. Consequently, for these printers, ink tanks of a type which directly accommodates ink are desirable in view of the reduced replacement frequency and increased ink containment efficiency of these ink tanks.
Printed matter obtained using such a graphic art printer needs not only to provide high image quality but also to offer light resistance and gas resistance because the printed matter is sometimes posted outdoors. In general, dye ink offers only low light and gas resistance and thus has difficulty providing robust images. On the other hand, pigment ink containing pigment as a color material offers high light and gas resistance and can thus provide robust images. Thus, graphic art printers and the like have recently used pigment ink.
However, in the pigment ink, pigment particles float dispersedly without being dissolved into a solution. The thus floating pigment particles start to sink down in the direction of gravitational force due to their own weight as time elapses with the ink tank left stationary. Thus, in the pigment ink in the ink tank, a distribution of concentration of the pigment particles is formed, with the pigment concentration increasing downward in the direction of gravitational force and decreasing upward in the direction of gravitational force. If such a distribution of concentration of the pigment particles is formed, the pigment concentration of the pigment ink ejected from the print head changes during an initial stage and a last stage of supply of ink from the ink tank to the print head. Hence, printed images may be subjected to color differences or color unevenness and offer degraded color stability and color reproducibility.
To allow the pigment particles of the pigment ink to be uniformly dispersed, a method for stirring pigment ink has been proposed. Japanese Patent Laid-Open No. 2004-306604 describes a configuration which stirs ink contained in an ink containing chamber formed inside a flexible bag positioned in a tank case. Pressurized air is introduced into a closed space formed between an inner surface of the tank case and an outer surface of the flexible bag to collapse the flexible bag. Thus, the ink in the ink containing chamber is pressurized and fed through an ink supply port to an ink supply system on a printing apparatus side. An ink supply path is formed in the ink tank so as to allow the ink containing chamber to communicate with the ink supply port. The pressurized ink in the ink containing chamber is guided through the ink supply path to the ink supply port. The ink supply path includes a buffer chamber which expands when the ink in the ink containing chamber is pressurized and which contracts when the ink is depressurized. The expansion and contraction of the buffer chamber is utilized to stir the ink in the ink containing chamber. That is, when the ink containing chamber is pressurized, the ink is drawn from the ink containing chamber into the buffer chamber. Then, when the ink containing chamber is depressurized to return the ink in the buffer chamber to the ink containing chamber, the ink is stirred by an ink flow generated in the ink containing chamber.
However, according to the method for stirring ink using the buffer chamber provided in the ink supply path as disclosed in Japanese Patent Laid-Open No. 2004-306604, the stirring performance depends on the shape or configuration of the ink tank or a mounted orientation of the ink tank. This may preclude ink containing pigment from being efficiently stirred.
For example, if the ink containing chamber extends a long distance along the direction of gravitational force and the buffer chamber is provided in the ink supply path between the ink supply port and an opening positioned at the bottom of the ink containing chamber, then sufficient stirring performance cannot be provided when the volume of the buffer chamber decreases at a low speed. That is, the ink flow squirted from the buffer chamber through the ink supply port and the opening toward an inner upper part of the ink containing chamber loses force and may fail to reach the inner upper part of the ink containing chamber.
Furthermore, if the ink containing chamber is of a horizontal type, the opening in communication with the ink supply path is formed in an inner side surface of the ink containing chamber which extends in the vertical direction. Thus, ink squirted from the buffer chamber through the ink supply path and the opening into the ink containing chamber flows in the horizontal direction. However, the pigment concentration of the ink in the ink containing chamber varies in the direction of gravitational force, and thus ink with the pigment concentration of an ink area corresponding to the position of the opening is temporarily introduced into the ink supply path and then squirted into the ink containing chamber with ink with the same concentration present therein. That is, ink squirted horizontally through the opening is provided to ink with the same pigment concentration and fails to act positively on ink with different pigment concentrations. Additionally, such horizontal ink ejection also slightly spatters the ink in the direction of gravitational force but achieves stirring at a lower level than when the ink is ejected in the direction of gravitational force. The thus slightly spattered ink is unlikely to reach the inner upper part of the ink containing chamber if the opening formed in the side surface of the ink containing chamber is positioned closer to the bottom of the ink containing chamber. In addition, if the opening formed in the side surface of the ink containing chamber is positioned in the middle of the ink containing chamber in the direction of gravitational force, the ink squirted horizontally through the opening into the ink containing chamber is not high but average in pigment concentration. Thus, in particular, an ink area with a low pigment concentration which is present in the inner upper part of the ink containing chamber is difficult to stir efficiently.
Possible methods for increasing the efficiency at which the ink in the ink containing chamber is stirred include increasing the volume of the buffer chamber provided in the ink supply path, and increasing the spring constant of a spring member which biases the buffer chamber to augment the amount of ink squirted and the force of the squirt. However, the increased volume of the buffer chamber increases the size of the ink tank. Furthermore, the increased spring constant of the spring member biasing the buffer chamber increases a pressure applied to ink in order to expand the volume of the buffer chamber. This requires increased pressure of pressurized air introduced into the tank case in order to pressurize the ink in the ink containing chamber. This results in the need to improve the capabilities of a pressurization pump on the printing apparatus side configured to supply the pressurized air, leading to increased size and cost of the printing apparatus. Additionally, the increased ink pressure requires increased thickness of the tank case and increased strength of a welded portion provided to form a closed space in the tank case. This may increase the size and cost of the ink tank.